Some components of vehicles, such as fuel cells, generate heat during normal operation, and require adequate cooling to dissipate the heat. One way of providing cooling is by way of a cooling plate containing a passage through which water or other coolant flows. The coolant is then pumped to an external heat exchanger to dissipate the heat absorbed by the coolant to the atmosphere. It is desired to maximize the coolant flow through the plate, and to maximize thermal contact between the coolant and the heat source. As a result, it is desired to produce a relatively thin cooling plate containing a relatively large-diameter tube with a serpentine shape.
One possible construction for these cooling plates is a curved tubular steel mold core inside a cast aluminum plate, and subsequently machined to produce the final shape of the cooling plate.
One method of molding cooling plates is by using a consumable-pattern casting method, such as lost-foam casting or lost-wax casting. Consumable-pattern casting allows the casting of parts with a more complex and more precise shape, which requires less machining to achieve the desired shape. However, this method presents difficulties with the positioning of the tubular core. A long, serpentine-shaped tube is desired to increase thermal contact with the coolant. This serpentine shape is prone to warping and deforming from the heat of the molten aluminum when it is poured into the mold, particularly in applications requiring a thin cooling plate and a correspondingly thin tube. The warping may create obstructions to coolant flow through the core, and may obstruct the flow of molten aluminum through the mold and prevent the aluminum from completely filling the mold. The warping may also cause the core to bend away from the central plane of the cooling plate. Due to the relative thinness of the cooling plate and thickness of the core, even small deviations from the plane result in the core being very near the surface of the cooling plate, in which case the core may be perforated during subsequent machining of the face of the cooling plate, rendering the casting unusable. In these cases, the cooling plate must be scrapped, resulting in added cost and waste of materials.
Referring to FIG. 1, one method of remedying this problem is to affix one or more support bars 10 directly to a serpentine tube 12 as shown in FIG. 1, to create a mold core 14 having increased rigidity to maintain its position and shape during the casting process. One drawback of this method is that the support bars 12 can obstruct the flow of molten aluminum through the mold and create porosity defects in the final casting. The resulting porosity defects can render the casting unusable, resulting in added cost and waste of materials. In addition, this method offers only limited support for the mold core, and it is still possible for the mold core to shift position away from the central plane of the cooling plate, resulting in the machining difficulties described above.
Therefore, there is a need for a method of manufacturing a consumable-pattern casting having reduced incidences of deformities in a tubular mold core, and reduced incidences of porosity defects.